1. Field of the Invention
The present invention relates to a resin composition which can be plated. The resin composition has superior plating characteristics and excellent electrical characteristics, and is particularly useful as a material for electric or electronic parts such as printed circuit boards, wiring circuit boards, connectors, housing, and insulators. More particularly, because the resin composition of the present invention is thermoplastic and has excellent plating and electrical characteristics, it is suitable as a material for manufacturing three dimensional circuit boards, molded interconnection devices (MID), and molded circuit boards (MCB) using injection molding techniques.
2. Discussion of the Background
Because thermoplastic resin compositions having superior plating characteristics can be easily processed by injection molding or extrusion molding into three dimensional articles, such compositions are abundantly used for various electric or electronic parts, automobile parts, mechanical parts, and ornamental articles.
Conventional resin compositions capable of being plated exhibit adequate plating characteristics due to improvements in the shape and size of fillers which are added to such compositions and development in the plating technology. In addition to the excellent plating characteristics thermoplastic resins used for electronic parts, such as printed circuit boards, wiring circuit boards, connectors, housing, and insulators, must have excellent electrical characteristics.
Here, the plating characteristics indicate the capability of connecting the plated resin composition and the plating metal, that is, the adhesion between the resin composition and the metal plating film. Excellent resin-metal adhesion means excellent plating characteristics. Excellent electrical characteristics, on the other hand, are characteristics required for an insulating resin material, particularly a high frequency insulating resin material. Specifically, a material having excellent electrical characteristics must have a low dielectric constant (.epsilon.) and a low dielectric loss tangent (tan .delta.).
However, conventional resins and resin compositions to be plated have a high dielectric constant and a high dielectric loss tangent. For example, resins to be plated disclosed in Japanese Patent Application Laid-open Nos. 136841/1981, 230276/1993, and 98637/1989 have excellent plating characteristics and possess an extremely high value industrially. However, because of their poor electrical characteristics, application of these resins must be limited. For example, it is difficult to use these resins for electronic parts used in the high frequency wave region due to a large signal loss.
On the other hand, the adhesion strength between a molded resin and a metal plating film is largely affected by the physical characteristics of the resin surface, that is, roughness of the resin surface. In particular, the plating adhesion strength is remarkably improved by forming uniformly small anchoring pores (hereinafter called "micropores"). This is called the anchoring effect.
In many cases, a chemical etching process using an acid, an alkali, or an organic solvent is used for forming micropores on the surface of molded resins. Such micropores can be easily formed by a chemical etching process which comprises, for example, manufacturing molded articles from a resin composition comprising a prescribed amount of inorganic filler which is soluble in an acid, an alkali, or an organic solvent and immersing the molded resin surface in a specific solvent (the acid, alkali, or organic solvent) to cause the inorganic filler to dissolve out and be removed.
In this manner a resin composition comprising a thermoplastic resin and a specific inorganic filler which is soluble in an acid, an alkali, or an organic solvent has been conventionally used as the resin composition to be plated. Various fillers, such as calcium carbonate, glass, magnesium carbonate, magnesium oxide, calcium pyrophosphate, barium sulfate, barium carbonate, and zinc oxide, are used as the inorganic filler. These conventional inorganic fillers, however, impair the electrical characteristics of the resins, for example, by increasing the dielectric constant or the dielectric loss tangent. The increase in the dielectric constant or the dielectric loss tangent causes the signal loss to increase or delays the signal transmission speed, particularly when the product is used as an insulating material for electronic parts, inter alia, electronic parts for high frequency wave signals.
Here, the high frequency signals are signals of a frequency in the range of 1 GHz or larger. Specific equipment using high frequency signals includes cellular phones, PHS, pocket bells, satellite terminals, navigation systems, wireless LANs, and the like.
Conventionally, there has been no report disclosing resin compositions having both excellent plating characteristics and excellent electrical characteristics (low dielectric constant and low dielectric loss tangent).
Because of miniaturization and high integration of electronic parts in recent years, great attention is given to the technologies for manufacturing electronic parts by injection molding which is suitable for molding small and integrated parts.
An object of the present invention is therefore to provide a thermoplastic resin composition for plating, suitable for injection molding and having both excellent plating characteristics and excellent electrical characteristics.
In view of this situation the present inventors have conducted extensive studies and found that the addition of a specific inorganic filler to a thermoplastic resin produces a resin composition exhibiting both excellent plating characteristics and excellent electrical characteristics.